1. Field of the Invention
The present invention relates to the improvement of a slush molding method and an apparatus therefor.
2. Description of the Prior Art
A slush molding method is a method of causing a resin in the state of sol or powder to adhere to the molding surface of a heated mold, forming a molten resin layer by removing the surplus resin, cooling and solidifying the resin, and removing the molded product from the mold. This method is suitable for the production of a molded product having a complicated shape. In this method, a fluidized-bed heating oven such as that described in Japanese Patent Laid-Open No. 139410/1985 as considered to be suitable as a heating means. More preferably, there is a slush molding apparatus such as the apparatus 10' shown in FIGS. 3 and 4 which is composed of a fluidized-bed oven 6 including a heating medium 7 and a mold dipping device 3 for dipping a mold 1. The fluidized-bed oven 6 of the slush molding apparatus 10' is filled with a heating medium 7 such as alumina beads, zircon sand and glass beads, and the heating medium 7 is heated by a heater 8 in the oven 6 and is fluidized by the air 9 introduced by a pipe provided in another chamber (not shown). The mold dipping device 3 has a chucking means for holding the mold 1 and a synchronous frame 4 to which a lid 11 is welded and which is so designed as to be situated above the mold 1 at the time of dipping the mold 1.
When a resin is subjected to slush molding by using the apparatus 10', the mold 1 charged with the resin in the state of powder or sol and conveyed to the apparatus 10' is chucked by the chucking means of the mold dipping device 3, and is dipped into the heating medium 7 and heated. After the molding surface of the mold 1 is covered with the molten resin, the surplus resin is discharged, and the solidified molded product is released from the mold 1.
In the above-described slush molding method, however, the heating medium 7 which is blown by the air 9 often enters the mold 1, because the mold 1 is lowered down to the vicinity of the upper surface of the heating medium 7 when the mold 1 is dipped into the heating medium in the oven 6. If the heating medium 7 enters the mold 1, the heating medium 7 adheres to the surface of the molded product, resulting in the production of a defective. Therefore, whenever the heating medium 7 enters the mold 1, the operation must be suspended to remove the heating medium 7, thereby greatly lowering the productivity.
As a measure for preventing the heating medium 7 from flying, the amount of air is reduced. The reduction in the amount of air, however, is disadvantageous in that it varies the temperature of the mold 1 too widely to preserve the uniformity of the molten state of the resin, thereby bringing about a problem of defective melting.